Thermally induced phase separated azlactone membrane

ABSTRACT

The present invention provides a microporous material or a membrane in which the membrane includes an azlactone moiety which is blended with or grafted to a thermoplastic polymer to provide a porous material having an internal structure characterized by a multiplicity of spaced, randomly disposed, non-uniform shaped, equiaxed particles of the polyazlactone polymer/thermoplastic polymer blends or the azlactone-graft copolymer. Each of the adjacent particles throughout the material are separated from one another to provide said material with a network of interconnected micropores and each of the particles are connected to each other by a plurality of fibrils. In addition to unmodified azlactone membranes, membranes which have been modified by subsequent reaction of the azlactone moiety with a suitable nucleophile are also included within the scope of the present invention. Preferred nucleophiles capable of reacting with an azlactone membrane of this invention include biologically significant nucleophiles such as amines, thiols and alcohols as well as amino acids, nucleic acids and proteins.

This is a continuation-in-part of Ser. No. 08/011,366, filed Jan. 29,1993, now abandoned.

The present invention is generally related to azlactone modifiedpolymeric membranes and is more particularly related to a thermallyinduced, phase separated polymeric membrane containing an azlactonemoiety which was added to the polymer by extrusion grafting or blending.The thermally induced, phase separated azlactone polymeric membranes aresuitable for use in a variety of separation and chromatographicapplications.

BACKGROUND

Polymeric supports which have been modified to include an azlactonemoiety may be useful for a number of applications. The capability of theazlactone moiety to covalently bind a variety of biologicallysignificant or useful materials to a polymer have allowed the use ofazlactone-modified polymers as complexing agents, enzymes, catalysts,polymeric reagents, and chromatographic supports as well as other typesof activated supports.

Methods to make azlactone-modified polymers are known. For example, EP 0392 735 published Oct. 17, 1990 reports suitable methods for attachingan azlactone moiety to a polymer, preferably a polymeric support such asa bead or membrane. The reported processes to produce azlactone modifiedpolymers or polymeric supports include mixing a suitable alkenylazlactone monomer with a polymer-producing monomer and copolymerizingthe mixture of monomers under conditions which do not compromise thereactive properties of the azlactone portion of the resulting copolymer.

Another reported method of attaching an azlactone moiety to a polymericsupport involves coating the surface of a polymerized substrate with anazlactone reagent. Reported processes provide a polymer having anazlactone moiety being covalently attached or bound to outer surfaces ofthe polymeric support. The covalent attachment of the azlactone moietyto the polymer avoids problems typically associated with surfacecoatings which are not bound to the polymer surface such as leaching ofthe coating from the polymer surface during the use of the coatedpolymer.

Another process for attaching an azlactone moiety to a polymeric supportis reported in EP 0 392 783 published Oct. 17, 1990. In this report, amonomeric 2-alkenyl azlactone moiety was extrusion grafted to apolyolefin base polymer. The process to prepare such a graft copolymerinvolved contacting a polyolefin base polymer with a free radicalinitiator system to give an activated polymer and then reacting theactivated polymer with a monomeric alkenyl azlactone moiety. The graftcopolymer prepared by the above process provided a polymeric supportthat had modified surfaces when compared to the base polymer and whichretained the desired physical and chemical properties of the azlactonemoiety. The reported azlactone graft copolymer may be extruded, formedor molded into a variety of configurations such as beads, pellets,strips, films, or wells and may be used in diverse applications such asthermoplastic adhesives and tie layers for barrier films. In addition,the azlactone moiety may be reacted with nucleophilic reagents such asproteins and other biologically active reagents. The covalent attachmentof biological reagents to the polymeric support through the graftedazlactone moiety allows use of the graft copolymers in separation andchromatographic applications.

Microporous films or membranes are one specialized type of materialwhich has potential application in a number of separation orchromatographic uses such as analysis of air, microbiological products,intravenous fluids or vaccines. A specific type of microporous film ormembrane is reported in U.S. Pat. No. 4,539,256 to Shipman. This patentreports a microporous film or sheet material that has a microporousstructure characterized by having a multiplicity of spaced, randomlydispersed, equiaxed, non-uniformly shaped particles of polymericmaterial that are connected to each other by a plurality ofthree-dimensionally dispersed polymeric fibrils.

A method of making this type of microporous film is also reported inU.S. Pat. No. 4,539,256. Briefly, the method of making such amicroporous film involves melt blending a crystallizable thermoplasticpolymer with a compound which is miscible with the polymer at themelting temperature of the polymer but that phase separates at atemperature at or below the crystallization temperature of the polymer.After the formation of the melt-blend, it is shaped into an article andthe article is then cooled to a temperature at which the polymercrystallizes and causes phase separation to occur between the polymerand the compound to give a two phase article. The compound used to formthe melt-blend is extracted or removed from the shaped article. Finally,the article is then oriented or stretched in a least one direction togive a network of particles interconnected with fibrils throughout thearticle.

Although the reported process of Shipman provides a specializedmicroporous structure, the process requires that the polymer used mustbe at least partially crystallizable and must be capable of phaseseparating from a readily removed compound which is used to form therequisite melt-blend. Thus, not all polymeric materials may be used withthe reported process to prepare membranes. Importantly, factors orprocesses expected to destroy or markedly effect the crystallinity of apolymeric material would not be expected to provide suitable polymericmaterials for use in the process reported by Shipman.

SUMMARY OF THE INVENTION

In spite of an expected detrimental effect on the crystallinityproperties of a base polymer caused by either grafting or blendingprocesses, the present invention provides a unique microporous membranematerial formed from an azlactone-modified thermoplastic composition.

In one embodiment, a microporous material or membrane is produced froman alkenyl azlactone moiety which is grafted onto a crystallizablethermoplastic polyolefin to provide a porous material having an internalstructure characterized by a multiplicity of spaced, randomly disposed,non-uniformly shaped, equiaxed particles of the azlactone graftcopolymer. Each of the adjacent particles throughout the material areseparated from one another to provide the material with a network ofinterconnected micropores. In addition, each of the particles areconnected to each other by a plurality of fibrils.

In another embodiment, a microporous material or membrane havingsubstantially the same properties as those listed above is produced froma polyazlactone homopolymer or copolymer which is extrusion blended witha crystallizable thermoplastic polyolefin.

Preferred alkenyl azlactone monomers suitable for use in extrusiongrafting or for use in preparing polyazlactone homopolymers orcopolymers suitable for use in extrusion blending include a compound ormonomer of the formula ##STR1## where R¹ is hydrogen or methyl and whereR² and R³ are, independently, alkyl having 1-14 carbon atoms, cycloalkylhaving 3-14 carbon atoms, aryl having 5-12 carbons atoms, arenyl having6-26 carbons atoms and 0-3 sulfur, nitrogen, and nonperoxidic oxygenatoms, or R² and R³ taken together with the carbon atom to which theyare attached form a carbocyclic ring having 4-12 carbon atoms. A highlypreferred alkenyl azlactone monomer is vinyl dimethyl azlactone.

Preferred base polymers for use in this invention include polyolefinssuch as polyethylene, polypropylene and polymethylpentene. A highlypreferred polymer is high density polyethylene.

In addition to azlactone-modified membranes having an intact azlactonemoiety bound to the base polymer, membranes which have been modified bysubsequent reaction of the azlactone moiety with a suitable nucleophileare also included within the scope of the present invention. Preferrednucleophiles capable of reacting with an azlactone membrane of thisinvention include biologically significant nucleophiles such as amines,thiols and alcohols as well as amino acids, nucleic acids and proteins.Particular preferred nucleophiles are biological active proteins such asantigens and antibodies.

Grafted or blended azlactone thermoplastic compositions are believed toproduce a microporous material or a membrane containing graftedazlactone monomer or blended polyazlactone polymer distributedthroughout the bulk of membrane rather than being distributed only onaccessible, exposed or outer surfaces of the membrane. The distributionof the azlactone moiety throughout the bulk of the membrane is alsobelieved to increase the available active sites on the membrane whichprovides a substantial increase in the binding capacity of the membranefor a variety of useful reagents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the process steps used to prepare amembrane of this invention.

FIG. 2 is a schematic diagram of an extrusion blending process using atwin screw extruder.

DETAILED DESCRIPTION

The present invention provides an azlactone membrane having a network ofspaced, randomly disposed, non-uniformly shaped, equiaxed particlesinterconnected with a plurality of fibrils to provide a network ofinterconnected particles containing dialkylazlactone moieties extrusiongrafted to or blended with a crystallizable thermoplastic polymer.

Suitable extrusion grafted azlactone thermoplastic compositions for usein this invention may be made according to the process reported in EP 0392 783 which is incorporated by reference herein for the purpose ofdescribing methods of preparing azlactone graft copolymers. Briefly, asuitable polyolefin resin such as high density polyethylene,polypropylene or polymethylpentene is mixed with a free radicalinitiator, such as a peroxide or azo initiator, and the mixture isheated in an extruder at a temperature sufficient to break down theinitiator and produce free radicals. The free radical initiator isselected from a variety of known compounds based on the properties ofthe polyolefin resin and the amount of added free radical initiator isselected to provide for sufficient grafting without causing undesiredside reactions such as cross-linking of the polyolefin resin. Typicalamounts of free radical initiator used to graft a vinyl dialkylazlactoneto a polyolefin resin are about 0.01-0.25 weight percent.

The free radicals produced then extract hydrogen atoms off of thepolyolefin resin. As the polyolefin resin loses hydrogen radicals, thepolyolefin resin is activated and may undergo several subsequentreactions such as crosslinking with other base polymers, degradation,oxidation or, significantly, reaction with a suitable alkenyl monomer.In the formation of the azlactone graft copolymer, after the polyolefinresin is activated, a vinyl dialkylazlactone monomer such as vinyldimethyl azlactone is injected into the extruder. The injected vinylazlactone monomer then covalently binds to the activated polyolefinresin and may be used to form a membrane.

As is reported in EP 0 392 783, the vinyl azlactone copolymer issusceptible to hydrolysis. Therefore, the grafting process and reactionare preferably done in the absence of water in an inert atmosphere or anunreactive environment. Use of these conditions prevents the azlactonefrom degrading and prevents side reactions from interfering with thegrafting or addition of the vinyl azlactone monomer to the polyolefinresin.

Suitable extrusion blended azlactone thermoplastic compositions for usein the this invention may be prepared according to the processesreported in pending U.S. patent application Ser. No. 08/119,036 filedSep. 9, 1993, which is incorporated by reference in the presentapplication for the purposes of describing the preparation of blendedazlactone thermoplastic compositions. Melt blending of polyazlactonehomopolymers or copolymers with thermoplastic polymers is an alternativeto the extrusion graft process described above. When polyazlactonepolymers are melt blended with thermoplastic polymers, a two phase,incompatible blended product usually results. This incompatibilitygenerally does not have deleterious properties of incompatiblecompositions due to the ability of azlactone-functionality to react withdesired biological ligands.

As described in the cited application, polyazlactone blends may beprepared from any thermoplastic polymer that is non-reactive with anazlactone monomer. Examples of thermoplastic polymers suitable for meltblending with polyazlactone homopolymers or copolymers includepolyamides (e.g., nylon 6), polyurethanes, polyacrylates,polymethacrylates, polystyrene, polyolefins, ethylene-vinyl acetatecopolymers, poly(N-vinyl lactams) (e.g., polyvinylpyrrolidone),polyvinyl acetates, polyoxyalkylenes, styrene-acrylonitrile copolymers,polyphenylene oxides, and polycarbonates (polyvinyl alcohol homopolymersand copolymers are not suitable because the hydroxy groups can reactwith azlactone). These thermoplastic polymers may be homopolymers orcopolymers. Thermoplastic copolymers may include azlactone copolymers,such as graft copolymers reported in U.S. Pat. No. 5,013,795 to Colemanet al. and bulk copolymers reported in U.S. Pat. No. 4,695,608 to Engleret al.

Polyazlactone polymers may be any compound containing or comprising atleast one azlactone moiety. Preferred polyazlactone polymers arehomopolymers of 2-alkenyl azlactone monomers. Suitable 2-alkenylazlactone monomers are known compounds, their synthesis being describedfor example in U.S. Pat. Nos. 4,304,705; 5,081,197 and 5,091,489 all toHeilmann et al. Suitable 2-alkenyl azlactones include:

2-ethenyl-4,4-dimethyl-1,3-oxazolin-5-one,

2-isopropenyl-4,4-dimethyl-1,3-oxazolin-5-one,

2-ethenyl-4-methyl-4-ethyl-1,3-oxazolin-5-one,

2-isopropenyl-4-methyl-4-butyl-1,3-oxazolin-5-one,

2-ethenyl-4,4-dibutyl-1,3-oxazolin-5-one,

2-isopropenyl-4-methyl-4-dodecyl-1,3-oxazolin-5-one,

2-isopropenyl-4,4-diphenyl-1,3-oxazolin-5-one,

2-isopropenyl-4,4-pentamethylene-1,3-oxazolin-5-one,

2-isopropenyl-4,4-tetramethylene-1,3-oxazolin-5-one,

2-ethenyl-4,4-diethyl-1,3-oxazolin-5-one,

2-ethenyl-4-methyl-4-nonyl-1,3-oxazolin-5-one,

2-isopropenyl-4-methyl-4-phenyl-1,3-oxazolin-5-one,

2-isopropenyl-4-methyl-4-benzyl-1,3-oxazolin-5-one,

2-ethenyl-4,4-pentamethylene-1,3-oxazolin-5-one, and

2-ethenyl-4,4-dimethyl-1,3-oxazolin-6-one. Most preferred 2-alkenylazlactones include 2-ethenyl-4,4-dimethyl-1,3-oxazolin-5-one (VDM) and2-isopropenyl-4,4-dimethyl-1,3-oxazolin-5-one. Other azlactone monomersinclude the 2-(4-alkenylphenyl)-5-oxazolones reported in U.S. Pat. No.5,039,813.

If a polyazlactone copolymer is to be formed, a comonomer having similaror different chemical or physical properties may be included, dependingon the desired characteristics for the copolymer to be blended.Nonlimiting examples of comonomers useful to be copolymerized withazlactone moieties to form copolymers include methyl methacrylate, vinylacetate, vinyl aromatic monomers, alpha,beta-unsaturated carboxylicacids or their derivatives or vinyl esters, vinyl alkyl ethers, olefins,N-vinyl compounds, vinyl ketones, styrene, or vinyl aldehydes.Nonlimiting examples of such comonomers are reported in EP 0 392 735 andEP 0 392 783.

Polyazlactone copolymers may be prepared by bulk polymerization asreported in U.S. Pat. No. 4,695,608 to Engler et al. In addition,polyazlactone polymers and oligomers may be typically prepared by freeradical polymerization of azlactone monomers, optionally with comonomersas described in U.S. Pat. No. 4,378,411.

Thermoplastic polymers are readily commercially available from a numberof sources. While thermoplastic polymers may be melt blended attemperatures ranging from about 50° C. to about 350° C., it is preferredthat thermoplastic polymers are melt blended at temperatures from about75° C. to about 300° C., and more preferably from about 100° C. to about300° C.

Melt blending of thermoplastic polymer with a polyazlactone homopolymeror copolymer may occur at temperatures which are required for themelting of the thermoplastic polymer. Because polyazlactone homopolymersgenerally do not degrade significantly at temperatures below about 275°C., there are no deleterious byproducts of the melt blending process.Preferably, to minimize discolorization, the melt blending should occurbelow about 210° C.

The temperature of melt blending must be at least at or above the glasstransition temperature (Tg) of both the polyazlactone homopolymer andthe thermoplastic polymer and preferably is at least about 25° C. abovethe Tg of amorphous or glassy polymers such as polystyrene orpolymethylmethacrylate and at least about 10° C. above the melting pointof semicrystalline polymers such as polyethylene and polypropylene.

Melt blending of polyazlactone homopolymers with a thermoplastic polymermay be done using a twin-screw extruder. As illustrated in FIG. 2, afterhomopolymerization of alkenyl azlactone, polyazlactone homopolymer (orother polyazlactone copolymer) in a pelletized form is introduced toextruder 30 from vessel 32. Thermoplastic polymer is introduced inpelletized form into extruder 30 from vessel 34. Vacuum ports 35 ventoff volatiles. If thermoplastic polymer were introduced into theextruder 30 in solution, then vacuum ports 35 would vent off the solventalso. Gear pump 36 eliminates surging and produces a continuous strandof the blended composition. The blended composition is quenched in bath37 which contains a cold (dry ice temperature) inert cooling fluid suchas FLUORINERT heat transfer liquid (3M, St. Paul, Minn.). Finally, thecooled, blended composition is directed through pelletizer 38.

Alternatively, other conventional mixing processes used in the art, suchas a Brabender mixer, may also be used.

The weight ratio of thermoplastic polymer to polyazlactone polymer mayrange from about 99.99:0.01 to about 50:50. Preferably, the weight ratioof thermoplastic polymer to azlactone polymer is about 95:5, when theazlactone polymer is azlactone homopolymer prepared according to themethod reported in EP 0 392 735.

In addition to polyazlactone homopolymers, any of the polyazlactonecopolymers and oligomers described in pending U.S. patent applicationSer. No. 08/119,036 may be used in melt blending with thermoplasticpolymer. These blends need not be compatible. However, the reactivity ofincompatible blends with biologically active substances is notcompromised by polymer blend incompatibility. Generally, the mixingconditions and temperature conditions for melt blending azlactonecopolymers are similar to melt blending azlactone homopolymers.

To make polyazlactone blends suitable for further processing, the meltblending of the azlactone-modified thermoplastic composition should notadversely alter bulk properties of the thermoplastic polymer. Melt flowindex is a key bulk property. The azlactone-modified composition mayhave a melt flow index (g/10 min.) ranging from within about 50% of themelt flow index of the thermoplastic polymer alone to within about 99%of the melt flow index of the thermoplastic polymer alone. Preferably,the melt flow index of the azlactone-modified composition is withinabout 75% of the melt flow index of the thermoplastic polymer alone.

After the azlactone graft or blend compositions are formed according toreported processes, these compositions may be formed into a microporousmembrane. According to the schematically illustrated steps of FIG. 1, anazlactone thermoplastic composition is starve-fed from hopper 10 intoextruder 14. The composition is formed into a melt-blend with a blendingcompound injected through port 12 in extruder 14.

Preferred blending compounds are typically solvents or mixtures ofsolvents which will form a homogeneous solution with the polymer at hightemperatures and will form two phases when the homogeneous mixture iscooled below the crystalline temperature of the composition. Forexample, mineral oil is a preferred solvent because it is capable offorming a homogeneous solution with polyolefins at high temperatures butthen forms two phases as the solution is cooled. The amount of blendingcompound which is mixed with the azlactone thermoplastic compositiondepends on the base polymeric resin. For example, the amount of mineraloil used to form a melt-blend of high density polyethylene is about55-80 weight percent, for polypropylene and polymethylpentene the amountof mineral oil used to form a melt-blend is about 30-75 weight percent.If desired, a small amount of nucleating agent such as pigments andpolysorbitol derivatives may be added to the melt-blend.

Extruder 14 is maintained at a temperature which is sufficient to form ahomogenous melt of the composition and blending compound. Generally thetemperature is set at a value which raises the temperature of themelt-blend above the melting temperature of the composition but whichdoes not cause thermal degradation of the composition. If needed,extruder 14 may contain a static mixer, not shown, to ensure that auniform, homogeneous melt-blend is obtained.

The extruder 14 is preferably configured so that when the melt-blendreaches a temperature greater than the melting point of the composition,the hot melt-blend is then extruded through die 16 onto cold roller orcasting wheel 18. The temperature of casting wheel 18 is maintained at atemperature below the melting point of the polymer so that themelt-blend forms two phases on contact with the casting wheel. Forpolyolefins the casting wheel is typically maintained at a temperatureof between 30°-180° C. Alternative casting wheels, such as patternedwheels, may also be used.

As the melt-blend cools it separates into a two phase system, theblending compound in one phase and the polymer composition in a secondphase. After the two phases are formed, the blending compound is thenseparated from the polymer in extractor 20. Extractor 20 preferably usesa solvent which is miscible with the blending compound and is alsopreferably a nonaqueous solvent. Suitable solvents includetrichloroethane and fluorinated hydrocarbons as well as mixtures offluorinated hydrocarbons. Preferably, the nonaqueous extraction solventis removed and recycled after being used to extract the blendingcompound from the cooled melt-blend.

After the blending compound has been extracted, the resulting matrix isdried in dryer 22 at an elevated temperature to insure complete removalof all of the extraction solvent. The dried matrix is then oriented inat least the machine direction in orienter 24 and then is preferablyoriented in the transverse direction in tenter 26. Typically, the driedmatrix is stretched in both the machine and transverse directions up toabout three-fold. The formation of the particles and connecting fibrilsare generally formed during the orienting process. Although orientationin both machine and traverse directions to provide a biaxially orientedmaterial is preferred, those of ordinary skill will understand that thedried matrix may be oriented in a single direction if desired.

After being oriented, the membrane is wound onto core 28. Theazlactone-containing membrane is preferably stored in the absence ofwater or water vapor in order to prevent hydrolysis or degradation ofthe azlactone.

The azlactone thermally induced, phase separated membranes of thepresent invention may be further modified with a variety of biologicallyuseful ligands. For example, ligands for use in the present membranesmay include biologically active materials having azlactone-reactive,nucleophilic functional groups. Nonlimiting examples of biologicallyactive materials are substances which are biologically,immunochemically, physiologically, or pharmaceutically active. Examplesof biologically active substances include proteins, peptides,polypeptides, antibodies, antigenic substances, enzymes, cofactors,inhibitors, lectins, hormones, receptors, coagulation factors, aminoacids, histones, vitamins, drugs, cell surface markers, and substanceswhich interact with them.

Of the biologically active substances, proteins, enzymes and antigenicsubstances are desired for coupling to the present azlactone-modifiedmembranes. Nonlimiting examples of proteins, enzymes, and antigenicsubstances include natural and recombinant Protein A, immunoglobulinssuch as rat, human, bovine, rabbit, and mouse, concanavalin A, bovineserum albumin, thyroglobulin, apoferritin, lysozyme, carbonic anhydrase,lipase, pig liver esterase, penicillin acylase, and bacterial antigen.Uses for immobilized proteins, enzymes and antigenic substances arereported in EP 0 392 735.

EXAMPLES

The following examples are provided to further illustrate the practiceof this invention but should not be construed to limit the scope of theappended claims. In the examples, the physical characteristics ofmembranes prepared according to the described process where determinedaccording to the following tests and procedures.

MEMBRANE TEST 1

Basis Weight (g/m²)

1. Cut or punch out a 10×10 cm sample.

2. Weigh sample to +/-0.001 g.

3. Multiply weight by 100 to give basis weight in g/m².

Thickness (μ:microns)

1. Measure with low pressure caliper gauge.

2. Convert from mils to microns (1 mil=25.4 microns).

Density (g/cm³)

1. Obtain basis weight and thickness values.

2. Divide basis weight by 10,000 to convert from g/m² to g/cm².

3. Divide micron thickness values by 10,000 to convert units frommicrons (μ) to centimeters (cm).

4. Divide converted basis weight by the converted thickness to givedensity as g/cm³.

MEMBRANE TEST 2

Water Wettability (Scale 1-5: # sec)

1. Punch out sample into a 47 mm diameter disk.

2. Fill a petri dish half full with water and add 10-15 drops of 1%(w/v) aqueous bromophenol blue indicator.

3. Using a stopwatch, determine the number of seconds (+/-0.1 s)required to wet-out the sample with the blue aqueous solution.

4. Use the following scale to determine the wetting characteristics ofthe membrane:

1) Uniformly wets instantly (<1 sec),

2) Uniformly wets slowly (report with time),

3) Partially wets instantly (<1 sec),

4) Partially wets slowly (report with time),

5) Hydrophobic; does not wet at all.

MEMBRANE TEST 3

Handleability (#C, #P)

1. Punch out a 47 mm diameter disk from sample.

2. Place disk in the palm of hand and crumple it into a ball for aperiod of 10 seconds.

3. Flatten the disk out and determine the number of cracks (#C) andpieces (#P) visible to the naked eye.

Tensile and Elongation

1. Determine tensile and elongation using ASTM D882-83 for both themachine (MD) and transverse (TD) directions.

MEMBRANE TEST 4

Water Flow Rate (cc/mm)

1. Punch out sample into a 47 mm diameter disk.

2. If the sample is water wettable (hydrophilic), go to step 3. If thesample did not wet-out (hydrophobic), immerse it in ethanol and thenrinse it with water directly before going to step 3.

3. Place sample into the Nucleopore Water Flow Chamber (Model 6005087,Nucleopore, Pleasanton, Calif.) and seal.

4. Fill chamber with 200 ml of distilled, deionized water.

5. Set pressure gauge to 10 psi.

6. Preweigh an empty beaker.

7. Open pressure valve to chamber and purge 25 ml of water into a wastebeaker.

8. Transfer outlet hose to preweighed beaker, start timer, collect 100ml of water, remove/replace preweighed beaker, and stop the timer.

9. Reweigh the beaker with the collected ≈100 ml and determine theweight of the collected water.

10. Use the following equation to determine the water flow rate:##EQU1##

Water Flux at 10 psi (cc/min·cm²)

1. Obtain a water flow rate value.

2. Divide the water flow rate value by the disk area (17.35 cm²) to givethe membrane's water flux value in units of cc/min·cm².

Permeance (cc/min·cm² ·psi)

1. Calculate the water flux value of the membrane.

2. Divide the water flux value by 10 psi in order to normalize it withrespect to pressure to give the permeance in units of cc/min·cm² ·psi.

Permeability Coefficient (cc·cm/min·cm² ·psi)

1. Calculate the permeance of the membrane.

2. Multiply the permeance value by the thickness (cm) of the membrane inorder to obtain its permeability coefficient.

MEMBRANE TEST 5

Pore Size (μ:microns)

The average pore size of the membrane sample was determined using ASTMF316-86 (Bubble Point).

Porosity (% Void)

Approximate the % void (porosity×100) of the sample by using thefollowing equation: ##EQU2##

EXAMPLE 1 Azlactone-Graft/High Density Polyethylene Membrane

The hopper of a 1 and 1/4 inch (32 mm) single screw extruder with sevenindependently controlled zones (Killion KN-125; Cedar Grove, N.J.) wasstarve fed with pellets of high density polyethylene (HDPE, Dow 8345N,Midland, Mich.). A solution containing initiator (50:50 weight:weightLUPERSOL 101 (2,5-dimethyl-2,5-di-(t-butylperoxy)hexane):LUPERSOL 130(2,5-dimethyl-2,5-di-(t-butylperoxy)hex-3-yne); AtoChem, Farmindale,N.Y.) in tetrahydrofuran (50:50) was dripped under a nitrogen atmosphereinto the extruder feed throat at a rate to provide 0.1 wt. % ofinitiator based on polymer weight. Monomeric2-ethenyl-4,4-dimethyl-2-oxazoline-5-one (VDM, available from SNPE, Inc,Princeton, N.J.) was fed in a port between barrel zones 3 and 4. Theextruder speed was set at 75 rpm and the feed rates were adjusted toprovide a total flow rate of 80 g/minute. The feed throat was watercooled.

Zones 1-7 were heated; Zone 1 at 150° C., Zone 2 at 160° C., Zone 3 at170° C., Zones 4 and 5 at 180° C., Zones 6 and 7 at 190° C., and the endadaptor at 190° C. The extrudate was quenched in a bath of fluorinatedcoolant (FLUORINERT heat transfer liquid, 41-2700-3246-3, available from3M, St. Paul, Minn.) and dry ice; then pelletized and stored under drynitrogen. The resulting grafted copolymer contained 3% by weight of VDM.

In the second stage, the grafted copolymer was introduced into thehopper of a 25 mm twin screw extruder (Model ZE 25, Berstorff, Hannover,Germany) fitted with a flat film die. The grafted copolymer was fed intothe extruder at a rate of 3.2 lb (1.5 Kg) per hour and the extruderoperated at a 8 lb (3.6 Kg) per hour throughput rate. Mineral oil(SUPERLA Mineral Oil 31-USP, Amoco, Chicago, Ill.) was introduced intothe extruder through an injection port at a rate to provide a blend of40% by weight of grafted copolymer and 60% by weight of mineral oil. Themixture was cast as a transparent film onto a smooth casting wheel at atemperature of 32° C. and a casting speed of 1.8 m/min. The extruderzone temperatures were as follows: Zone 1 at 196° C., Zones 2 and 3 at265° C., Zone 4 at 216° C., Zones 5-9 at 165° C. The film was washed ina metal frame with 1,1,1-trichloroethane for 15 minutes then air-driedat ambient temperature in a vented hood. It was biaxially stretched at1.5 times its original length/width with a film stretcher (TMLongStretcher, Somerville, N.J.) at 74° C. The resulting film was storedin a desiccator. The physical characteristics of this membrane arelisted in Table 1.

EXAMPLE 2 Azlactone-Graft/High Density Polyethylene Membrane

Using the method of Example 1, a copolymer containing 5% by weight ofVDM grafted onto high density polyethylene (Dow 8345N, Midland, Mich.)was prepared. The resulting graft copolymer was then made into a filmusing the procedures described in Example 1 and stored in a desiccator.The physical characteristics of this membrane are listed in Table 1.

EXAMPLE 3 Azlactone-Graft/Polypropylene Membrane

Using the general method of Example 1 except that a twin screw extruder(Model ZE-40x40D, Bertstorff, Hannover, Germany) was used and theprocessing zones were maintained at 180° C., a copolymer containing 3%by weight of VDM grafted onto polypropylene (PP, PRO-FAX 6723, HIMONT,Willmington, Del.) was prepared. Using the general method of Example 1with only 50% by weight mineral oil, 49.5% by weight VDM graftedpolypropylene and 0.5% by weight of a polyol acetal nucleating agent(MILLAD 3905, Milliken Chemical Spartanburg, S.C.) based on polymer,this copolymer was made into a film, washed with HCFC-123 (VERTREL 423,DuPont, Willington, Del.) then stored in a desiccator withoutorientation. The physical characteristics of this membrane are listed inTable 1.

EXAMPLE 4 Azlactone-Graft/Polymethylpentene Membrane

Using the general method of Example 1, except that a twin screw extruder(Model ZE40x40D, Bertstorff, Hannover, Germany) was used with theprocessing zones maintained at 260° C. and the initiator system was 50%by weight of 25:25:50 LUPERSOL 101:LUPERSOL 130:cumene hydroperoxide(AtoChem, Farmington, N.Y.) in tetrahydrofuran, a copolymer containing3% by weight of VDM grafted onto polymethylpentene (TPX, MitsuiPetrochemical Industries, Ltd., Tokyo, Japan) was prepared. Using thegeneral method of Example 1, this copolymer was made into a film at 232°C., washed with HCFC-123 (Vertrel 423, DuPont, Willington, Del.),biaxially stretched at 138° C., and stored in a desiccator. The physicalcharacteristics of this membrane are listed in Table

                                      TABLE 1                                     __________________________________________________________________________    Azlactone-Graft-Polyolefin Membrane Properties                                            3 wt. % 5 wt. % 3 wt. %                                                                             3 wt. %                                                 VDM-g-HDPE                                                                            VDM-g-HDPE                                                                            VDM-g-PP                                                                            VDM-g-TPX                                               1.5 × 1.5 stretch                                                               1.5 × 1.5 stretch                                                               0 × 0 stretch                                                                 1.5 × 1.5 stretch                     Property    Example 1                                                                             Example 2                                                                             Example 3                                                                           Example 4                                   __________________________________________________________________________    Azlactone Conc. (wt. %)                                                                   3       5       3     3                                           Bound Protein                                                                             150.0 (PBS)                                                                           143.8 (PBS)                                                                           70.2 (SO.sub.4)                                                                     60.3 (SO.sub.4)                             (μg rPA/cm.sup.2)                                                                      150.3 (SO.sub.4)                                                                      104.4 (SO.sub.4)                                          % SDS Resistance                                                                          49.5 (PBS)                                                                            46.4 (PBS)                                                                            28.3 (SO.sub.4)                                                                     6.6 (SO.sub.4)                                          49.4 (SO.sub.4)                                                                       50.6 (SO.sub.4)                                           Coupled Protein                                                                           74.1 (PBS)                                                                            66.7 (PBS)                                                (μg rPA/cm.sup.2)                                                                      74.4 (SO.sub.4)                                                                       52.8 (SO.sub.4)                                                                       20.4 (SO.sub.4)                                                                     3.9 (SO.sub.4)                              Basis Weight (g/m.sup.2)                                                                  7.0     7.2     75.7  34.9                                        Thickness (μm)                                                                         76.2    76.2    124.5 119.4                                       Density (g/cm.sup.3)                                                                      0.092   0.094   0.608 0.292                                       Wettability (scale 1-5)                                                                   5       5       5     5                                           Handleability (#C; #P)                                                                    0C, 1P  0C, 1P  10C, 5P                                                                             7C, 1P                                      MD Tensile (psi)                                                                          665     666     633   785                                         TD Tensile (psi)                                                                          696     675     586   817                                         MD Elongation (%)                                                                         116     118     35    11                                          TD Elongation (%)                                                                         81      92      43    23                                          Water Flux (cc/min. · cm.sup.2)                                                  1.54    0.37    0     2.91                                        Permeability Coef.                                                                        0.0012  0.0003  --    0.0410                                      (cc · cm/min. · cm.sup.2  · psi)                   Max. Pore Size (μm)                                                                    0.24    0.17    <0.10 0.48                                        Porosity (% Void)                                                                         90.4    90.1    32.7  67.7                                        __________________________________________________________________________     PBS  phosphate buffered solution                                              SO.sub.4  sulfate buffered solution                                      

EXAMPLE 5 Polyazlactone/High Density Polyethylene Blends andPolyazlactone/Polypropylene Blends

A 35% solids solution of azlactone homopolymer (solid powder having anaverage number molecular weight of about 11,000 prepared by solutionpolymerization of VDM (SNPE) with 0.5 wt. % azobisisobutyronitrile (VAZO64) in tetrahydrofuran) in tetrahydrofuran was blended with polyolefinin a corotating twin screw extruder (Model ZE-40X40D, Bertstorff,Hannover, Germany; rpm 109, amps 31, volts 108, zone temperatures: Zone1--25° C., Zones 2-4--180° C., Zone 5--170° C., Zone 6--180° C., Zone7--177° C., Zone 8--125° C., Zone 9--195° C., Zone 10--200° C., Zone11--205° C.). The polyolefin, high density polyethylene (9255 Hoechst)or polypropylene (6723 HiMont Pro-Fax), was solids fed into the feedthroat of the extruder using a K-tron weigh feeder. Also fed into thefeed throat of the extruder was a 35% solids solution of azlactonehomopolymer in tetrahydrofuran using a Gilson High Pressure LiquidChromatography Pump. Flow rates of the pump were adjusted to yield 2.5%azlactone homopolymer (8.1 ml/min) and 5.0% azlactone homopolymer (16.2ml/min) in the polyolefin to produce 15 lb/hr of the blended material.The weigh feeder was also set at 15 lb/hr. A vacuum port was used atzone 9 of the extruder to pull off any volatiles in the material. Theblend was extruded as a strand into a cold (dry ice) FLUORINET liquidsolution (3M, St. Paul, Minn.) where the strand was quenched andpelletized using a Conair pelletizer (Con Air Group of Bay City, Mich.).

EXAMPLE 6 Preparation of Polyazlactone/High Density PolyethyleneMembranes and Polyazlactone/Polypropylene Membranes

Using the general method of Example 1 (except that a twin screw extruderwas used, Model ZE-40X40D, Bertstorff, Hannover, Germany havingprocessing temperature zones as follows: Zone 1--248° C., Zone 2--271°C., Zone 3--271° C., Zone 4--248° C., and Zone 5--177° C.) the blendedazlactone compositions were made into films. In addition, whenpolypropylene was the base polymer, the weight percent of blendedpolymer was 35 wt. % and the weight percent of mineral oil was 65 wt. %.The physical characteristics of the blended azlactone films are listedin Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Azlactone-Blend-Polyolefin Membrane Properties                                           HDPE  2.5 wt. %                                                                            2.5 wt. %                                                                            5 wt. %                                                                              5 wt. %      2.5 wt. %                             Control                                                                             VDM-b-HDPE                                                                           VDM-b-HDPE                                                                           VDM-b-HDPE                                                                           VDM-b-HDPE                                                                           PP    VDM-b-PP                                                                            5.0 wt. %                       1.5 × 1.5                                                                     1.5 × 1.5                                                                      2.25 × 2.25                                                                    1.5 × 1.5                                                                      2.25 × 2.25                                                                    Control                                                                             1.5 × 1.5                                                                     VDM-b-PP             Property   stretch                                                                             stretch                                                                              stretch                                                                              stretch                                                                              stretch                                                                              0 × 0                                                                         stretch                                                                             0 × 0                                                                   stretch              __________________________________________________________________________    Polyazlactone                                                                            0     2.5    2.5    5.0    5.0    0     2.5   5.0                  Conc. (wt. %)                                                                 Bound Protein                                                                            66.7  62.2   75.1   47.4   57.7   130.5 170.0 159.3                (μg rPA/cm.sup.2)                                                          in SO.sub.4                                                                   % SDS Resistance                                                                         6.5   6.3    4.4    12.3   8.5    1.6   4.2   11.2                 Coupled Protein                                                                          4.3   3.9    3.2    5.8    4.9    2.2   7.3   17.8                 (μg rPA/cm.sup.2)                                                          in SO.sub.4                                                                   Basis Weight                                                                             39.5  84.6   38.2   89.6   39.4   46.7  68.0  140.2                (g/m.sup.2)                                                                   Thickness (μm)                                                                        94.0  182.4  114.3  188.0  124.5  94.0  268.2 355.6                Density (g/cm.sup.3)                                                                     0.420 0.463  0.456  0.477  0.316  0.497 0.253 0.394                Wettability                                                                              5     5      5      5      5      5     5     5                    (scale 1-5)                                                                   Handleability                                                                            0C, 1P                                                                              0C, 1P 0C, 1P 0C, 1P 1C, 1P 0C, 1P                                                                              0C, 1P                                                                              >10C, >10P           (#C; #P)                                                                      MD Tensile (psi)                                                                         2738  1844   2529   1688   2120   2781  404   225                  TD Tensile (psi)                                                                         2414  1846   2236   1842   2008   2403  458   176                  MD Elongation (%)                                                                        1683  1565   796    1356   747    762   18    19                   TD Elongation (%)                                                                        1473  1485   835    1418   762    616   28    15                   Water Flux 0.44  0.23   0.91   0.15   0.80   0.67  1.93  0                    (cc/min. · cm.sup.2)                                                 Permeability Coef.                                                                       0.0004                                                                              0.0004 0.001  0.0003 0.001  0.0006                                                                              0.0005                                                                              0                    (cc · cm/min. · cm.sup.2  · psi)                   Max. Pore Size (μm)                                                                   0.14  0.12   0.19   0.12   0.17   0.15  1.16  0.73                 Porosity (% Void)                                                                        56.0  52.2   65.0   50.0   66.9   46.6  72.7  57.6                 __________________________________________________________________________

EXAMPLE 7 Comparative Example

Three control samples were prepared in a similar fashion to the secondstage of Example 1. The three base resins (high density polyethylene8354N: Dow; polypropylene: Profax 6723: HiMont; polymethylpentene:Mitsui Petrochemical Industries, Ltd., Tokyo, Japan) were not grafted,but merely processed into membranes. In the case of polypropylene, aMillad nucleating agent (0.5 weight % based on polymer) and 50 weight %of mineral oil in place of the VDM grafted resins, were used. Thephysical properties of the three membranes which did not containazlactone are listed in Table 3.

The ability of the membranes described in Examples 1-4 and 6 to bindprotein was determined using the following procedure. Protein A(Repligen, Cambridge, Mass.) was radioiodonated with NaI¹²⁵ usingIodo-Beads (Pierce Chemical Co., Rockford, Ill.) and diluted to give aspecific radioactivity of 4900-5800 cpm/μg of protein dissolved inbuffer with a final protein concentration of 250 μg/ml. Two differentbuffers were employed. The PBS buffer contained 25 mM sodium phosphateand 150 mM sodium chloride with a pH of 7.5. The sulfate buffercontained 25 mM sodium phosphate and 1.5 M sodium sulfate with a pH of7.5. Discs (8 mm diameter) were punched from each film using a standardoffice paper punch. Each disc was placed in a 2.0 ml polypropylenemicrofuge tube then incubated with 200 μL of Protein A solution for 2hours at ambient temperature with rocking. Each blend and control wererun in triplicate. After 2 hours the protein solution was removed andunreacted azlactone was inactivated by incubating the disc with 1.0 Methanolamine (500 μL solution in 25 mM sodium phosphate, pH 9.0) for 1hour with rocking. All discs were rinsed for a minimum of 15 minuteswith 500 μL of the PBS buffer. Bound radioactivity was determined with aPackard Gamma Scintillation Spectrometer (Model 5230; PackardInstruments, Downers Grove, Ill.). Following the initial radioactivitydetermination, the discs were incubated with 500 μL of a 1% aqueoussolution of sodium dodecyl sulfate (SDS) for 4 hours at 37° C. The discswere rinsed 3 times with warm SDS solution and the residualradioactivity was determined. SDS is a protein denaturing detergent andserves to remove adsorbed (as opposed to covalently coupled) proteinfrom the film. The protein binding capabilities of the membranes arelisted in Tables 1, 2 and 3 are summarized in Tables 4 and

                                      TABLE 3                                     __________________________________________________________________________    Polyolefin Membrane Properties                                                Property           HDPE Control                                                                         PP Control                                                                           TPX Control                                  __________________________________________________________________________    Azlactone Conc. (wt. %)                                                                          0      0      0                                            Bound Protein      138.0 (PBS)                                                                          138.0 (PBS)                                         (μg rPA/cm.sup.2)                                                                             119.9 (SO.sub.4)                                                                     119.9 (SO.sub.4)                                                                     69.4 (SO.sub.4)                              % SDS Resistance   2.4 (PBS)                                                                            2.4 (PBS)                                                              2.2 (SO.sub.4)                                                                       2.2 (SO.sub.4)                                                                       1.1 (SO.sub.4)                               Coupled Protein    3.3 (PBS)                                                                            3.3 (PBS)                                           (μg rPA/cm.sup.2)                                                                             2.6 (SO.sub.4)                                                                       2.6 (SO.sub.4)                                                                       0.8 (SO.sub.4)                               Basis Weight (g/m.sup.2)                                                                         8.0    8.0    32.3                                         Thickness (μm)  76.1   76.1   114.3                                        Density (g/cm.sup.3)                                                                             0.105  0.105  0.283                                        Wettability (scale 1-5)                                                                          5      5      5                                            Handleability (#C; #P)                                                                           OC, 1P OC, 1P OC, 1P                                       MD Tensile (psi)   682    682    1104                                         TD Tensile (psi)   765    765    942                                          MD Elongation (%)  153    153    25                                           TD Elongation (%)  120    120    26                                           Water Flux (cc/min. · cm.sup.2)                                                         1.10   1.10   1.40                                         Permeability Coef. (cc · cm/min. · cm.sup.2  ·     psi)               0.0008 0.0008 0.0816                                       Max. Pore Size (μm)                                                                           0.18   0.18   0.37                                         Porosity (% Void)  89.0   89.0   68.8                                         __________________________________________________________________________     PBS  phosphate buffered solution                                              SO.sub.4  sulfate buffered solution                                      

                                      TABLE 4                                     __________________________________________________________________________    Protein Binding Capacity                                                               3 wt. %                                                                              5 wt. %                                                                              3 wt. %                                                                             3 wt. %                                                   VDM-g-HDPE                                                                           VDM-g-HDPE                                                                           VDM-g-PP                                                                            VDM-g-TPX          TPX                           Property Example 1                                                                            Example 2                                                                            Example 3                                                                           Example 4                                                                           HDPE Control                                                                         PP Control                                                                          Control                       __________________________________________________________________________    Bound Protein                                                                          150.0 (PBS)                                                                          143.8 (PBS)        138.0 (PBS)                                                                          138.0 (PBS)                         (μg rPA-cm2)                                                                        150.3 (SO.sub.4)                                                                     104.4 (SO.sub.4)                                                                     70.2 (SO.sub.4)                                                                     60.3 (SO.sub.4)                                                                     119.9 (SO.sub.4)                                                                     119.9 (SO.sub.4)                                                                    69.4 (SO.sub.4)               % SDS Resistance                                                                       49.5 (PBS)                                                                           46.4 (PBS)         2.4 (PBS)                                                                            2.4 (PBS)                                    49.4 (SO.sub.4)                                                                      50.6 (SO.sub.4)                                                                      28.3 (SO.sub.4)                                                                     6.6 (SO.sub.4)                                                                      2.2 (SO.sub.4)                                                                       2.2 (SO.sub.4)                                                                      1.1 (SO.sub.4)                Coupled Protein                                                                        74.1 (PBS)                                                                           66.7 (PBS)         3.3 (PBS)                                                                            3.3 (PBS)                           (μg rPA/cm2)                                                                        74.4 (SO.sub.4)                                                                      52.8 (SO.sub.4)                                                                      20.4 (SO.sub.4)                                                                     3.9 (SO.sub.4)                                                                      2.6 (SO.sub.4)                                                                       2.6 (SO.sub.4)                                                                      0.8 (SO.sub.4)                __________________________________________________________________________     PBS  phosphate buffered solution                                              SO.sub.4  sulfate buffered solution                                      

                                      TABLE 5                                     __________________________________________________________________________    Protein Binding Capacity                                                                      2.5 wt. %                                                                             5 wt. %                                                                              5 wt. % 2.5 wt. %                                      2.5 wt. %                                                                             VDM-b-HDPE                                                                            VDM-b-HDPE                                                                           VDM-b-HDPE                                                                            VDM-b-PP                                                                            5 wt. %                                                                             HDPE                               VDM-b-HDPE                                                                            1.5 × 1.5                                                                       1.5 × 1.5                                                                      2.5 × 2.5                                                                       1.5 × 1.5                                                                     VDM-b-PP                                                                            Control                                                                             PP                           1.5 × 1.5 stretch                                                               stretch stretch                                                                              stretch stretch                                                                             No stretch                                                                          1.5 × 1.5                                                                     Control              Property                                                                              Example 6                                                                             Example 6                                                                             Example 6                                                                            Example 6                                                                             Example 6                                                                           Example 6                                                                           stretch                                                                             No                   __________________________________________________________________________                                                             stretch              Bound Protein                                                                         62.2 (SO.sub.4)                                                                       75.1 (SO.sub.4)                                                                       47.4 (SO.sub.4)                                                                      57.7 (SO.sub.4)                                                                       170.0 (SO.sub.4)                                                                    159.3 (SO.sub.4)                                                                    66.7                                                                                130.5                                                                         (SO.sub.4)           (μg rPA-cm2)                                                               % SDS   6.3 (SO.sub.4)                                                                        4.4 (SO.sub.4)                                                                        12.3 (SO.sub.4)                                                                      8.5 (SO.sub.4)                                                                        4.2 (SO.sub.4)                                                                      11.2 (SO.sub.4)                                                                     6.5 (SO.sub.4)                                                                      1.6 (SO.sub.4)       Resistance                                                                    Coupled Protein                                                                       3.9 (SO.sub.4)                                                                        3.2 (SO.sub.4)                                                                        5.8 (SO.sub.4)                                                                       4.9 (SO.sub.4)                                                                        7.3 (SO.sub.4)                                                                      17.8 (SO.sub.4)                                                                     4.3 (SO.sub.4)                                                                      2.2 (SO.sub.4)       (μg rPA/cm2)                                                               __________________________________________________________________________     PBS  phosphate buffered solution                                              SO.sub.4  sulfate buffered solution                                      

We claim:
 1. A microporous membrane comprising crystallizable extrusiongrafted azlactone thermoplastic composition having an azlactonefunctional monomer extrusion grafted to a thermoplastic polymer, whereinthe microporous material has sufficient crystallinity to thermallyinduce phase separate, and has an internal structure characterized by amultiplicity of spaced, randomly disposed, non-uniformly shaped,equiaxed particles of the extrusion grafted azlactone thermoplasticcomposition, adjacent particles throughout the material being separatedfrom one another to provide the material with a network ofinterconnected micropores and being connected to each other by aplurality of fibrils of the extrusion grafted azlactone thermoplasticcomposition.
 2. A membrane having a network of spaced, randomlydisposed, non-uniformly shaped equiaxed particles interconnected with aplurality of fibrils to provide a network of interconnected microporescomprising vinyl dimethylazlactone extrusion to a thermoplastic polymerhaving sufficient crystallinity to thermally induce phase separate. 3.The membrane of claim 1 wherein the thermoplastic polymer is selectedfrom the group consisting of high density polyethylene, polypropylene,polymethylpentene, or mixtures thereof.
 4. The membrane of claim 1wherein the thermoplastic polymer is selected from the group consistingof high density polyethylene, polypropylene, polymethylpentene, ormixtures thereof.
 5. A method of making an azlactone-modified thermallyinduced phase separated membrane comprisinga) forming anazlactone-modified composition, wherein said composition comprises athermoplastic polymer having sufficient crystallinity to thermallyinduce phase separate, b) forming a membrane by mixing theazlactone-modified composition of a) with a blending compound at anelevated temperature to give a homogeneous melt-blend, c) forming atwo-phase article from the melt-blend, d) removing the blending compoundfrom the two-phase article, and e) orienting the article in at least onedirection to give an oriented membrane.
 6. The method of claim 5 whereinthe azlactone-modified composition is a crystallizable extrusion graftedazlactone composition of claim
 1. 7. The method of claim 5 wherein theazlactone polymeric material is formed by contacting an activatedpolyolefin with an alkenyl azlactone monomer selected from the groupconsisting of ##STR2## wherein R¹ is hydrogen or methyl and wherein R²and R³ are, independently, alkyl having 1-14 carbon atoms, cycloalkylhaving 3-14 carbon atoms, aryl having 5-12 carbon atoms, arenyl having6-26 carbon atoms and 0--3 sulfur, nitrogen, and nonperoxidic oxygenatoms, or R² and R³ taken together with the carbon atom to which theyare attached form a carbocyclic ring having 4-12 carbon atoms.
 8. Themethod of claim 5 wherein the blending compound is mineral oil.
 9. Themethod of claim 8 wherein the mineral oil is removed from the two-phasearticle by extraction.
 10. The method of claim 5 wherein the article isa two-phase film.
 11. The method of claim 5 wherein the membrane isbiaxially oriented.